Thermally stabile materials having high specific surfaces

ABSTRACT

The invention relates to materials which are stable at high temperatures and which have high specific surfaces. Said materials are produced by heating them to a temperature in a matrix above the later temperature at which they are used, e.g. aluminum oxide or zirconium oxide. The temperature of the specific surfaces thereof, after relatively long tempering, is 1100° C. or 1000° C., even above 50 m 2 /g or 10 m 2 /g. Carrier catalysts can be also be produced according to said method.

The present invention describes thermally stable materials having highspecific surface areas, and a method for production thereof.

Materials having high specific surface areas are of great technicalimportance in many sectors. For instance, aluminum oxides and zirconiumoxide-based materials, for example, are used as washcoats in automobileexhaust catalysts to achieve high dispersion of the noble metalcomponent (E. S. J. Lox, B. H. Engler, Handbook of HeterogeneousCatalysis, Wiley VCH, Weinheim 1997, 1559 ff). For chemistry catalystsalso, high specific surface areas are of great importance to ensure ahighest possible activity for the catalyzed reaction.

For instance, oxides having specific surface areas of about 100 m²/g canbe obtained by precipitation or coprecipitation of the correspondinghydroxides from salt solutions and subsequent calcination [M. Daturi etal., J. Phys. Chem. 2000, 104, 9186, M. F. L. Johnson, J. Mooi, J.Catal. 1968, 10, 342; G. K. Chuah, et al. Micoropor. Mesopor. Mater.2000, 37, 345; M. A. Valenzuela et al., Appl. Catal. A: General 1997,148, 315; G. Busca et al., Chem. Mater. 1992, 4 595; A. Alejandre etal., Chem. Mater. 1999, 11, 939; R. Roesky et al., Appl. Catal. A:General 1999, 176, 213; J. M. Lee et al. U.S. Pat. No. 4,446,201 1984].Higher specific surface areas 100-300 m²/g are achievable ifcorresponding precursor phases are produced by sol-gel processes beforethe calcination, customarily alkoxides or other organic metal compoundsbeing used [A. C. Pierre et al., Langmuir 1998, 14, 66; E. Elaouli etal., J. Catal. 1997, 166, 340; Y. Mizushima, M. Hon, J. Mater. Res.1993, 8, 2993; K. Maeda et al. J. Chem. Soc. 1992, 88, 97; M. A.Valenzuela et al., Appl. Catal. A: General 1997, 148, 315; C. OteroAréan et al., Mater. Lett. 1999, 39, 22; G. Busca et al., Catal. Today1997, 33, 239-249; E. Escalona Platero et al., Res. Chem. Intermed.1999, 25, 187]. The size of the specific surface areas is determined bythe particle size of the oxides formed, with smaller particles, based onthe weight of the sample, resulting in larger surface areas.

However, the materials which are used for the abovementionedapplications typically lose their high specific surface areas bysintering processes or phase transitions under high-temperaturetreatments, as can occur, for instance, in automobile exhaust gas underlong full-load operation, which highly adversely affect their serviceproperties (E. S. J. Lox, B. H. Engler, Wiley-VCH, Weinheim 1997,Handbook of Heterogeneous Catalysis, 1615). There is therefore aninterest in developing materials, the high specific surface area ofwhich is retained even at high temperatures.

Methods are known for producing oxides of high specific surface area,for example of ZrO₂ or CeO₂ZrO₂, in which the materials are producedfrom a precursor in the pores of a matrix, for example activated carbonor cellulose [M. Ozawa, M. Kimura, J. Mater. Sci. Lett. 1990, 9, 446; A.N. Shigapov et al., Appl. Catal. A, General, 2001, 210, 287]. Aluminatescan also be formed by thermal treatment of ion-exchanged zeolites.Calcining transition metal-exchanged zeolites produces spinel particlesin a silicate matrix which, after dissolution of the matrix, havesurface areas up to 200 m²/g [W. Schmidt, C. Weidenthaler, Chem. Mater.2001, 13, 607; T. Ogushi, JP 62-265114A, 1988].

Zeolites have also been produced in the pores of activated carbons (C.Madsen, C. J. H. Jacobsen, Chem. Commun. 1999, 673) or activated carbonshave been used in a complex method as exotemplates utilizingsupercritical fluids for the synthesis of nanoparticles (H. Wakayama etal. Chem. Mater. 2001, 13, 2392). In all mentioned routes based onactivated carbons or cellulose, the matrix, however, is removed bycombustion without further measures, as a result of which the materialsproduced have no particular thermal properties.

For instance, the oxide, according to the method of Ozawa and Kimura [M.Ozawa, M. Kimura, J. Mater. Sci. Lett. 1990, 9, 446] is formed in thecombustion of the activated carbon at temperatures which are in therange of the later service temperatures or even below. The oxidesproduced in this manner typically sinter at temperatures which are abovethe combustion temperature of the carbon, as a result of which theirspecific surface areas are drastically decreased. A similar situationapplies to the particles which are formed from zeolite precursors, whichparticles at relatively high temperatures or relatively long thermaltreatment grow to very large crystallites in the silicate matrix, as aresult of which their specific surface area is drastically decreasedaleady at their formation [C. Weidenthaler, W. Schmidt, Chem. Mater.2000, 12, 3811]. The matrix, in this method, does not have a limitingaction on particle growth.

The object underlying the present invention was to produce a method forproducing materials having high surface areas, which materials have athermal stability such that the surface area changes scarcely or onlyvery little, compared with the materials known from the prior art attheir service temperature.

It has now surprisingly been found that sintering and phase transitioncan be avoided at high temperatures if the materials are already treatedin their production at temperatures which are above the later servicetemperature.

The present invention therefore relates to a method for producing amaterial having a high specific surface area at high servicetemperature, the material, embedded in a matrix, being produced bythermal pretreatment, and the matrix then being removed, characterizedin that the thermal pretreatment comprises heating to a temperaturewhich is above the service temperature.

The thermal pretreatment is here preferably performed in a matrix inwhich the particles of the material or precursor thereof are enclosed insuch a manner that sintering is prevented. Such a matrix is preferablyselected from materials which may again be removed chemically orphysically after the formation of the material of high specific surfacearea produced according to the invention. Suitable examples of matrixmaterials can be selected, for example, from finely divided carbonaceousmaterials, such as activated carbon and ordered carbons, and/or fromsilica gels, in particular ordered silica gels.

The matrix materials can be removed, for example, by reaction with areactive gas, such as by converting these materials into gaseouscompounds, for example when the reactive gas is oxygen, by combustion,or by dissolving the matrix materials by suitable agents, for exampleusing strong acids or alkali solutions. If a carbonaceous material isused as matrix, the combustion to give CO₂ has proved a suitable methodfor removal thereof. Silica gels and similar materials can be removed,for example, by dissolution with strong acids or alkali solutions, suchas HF or NaOH.

In a preferred embodiment, the precursor for the material having a highspecific surface area is applied to the matrix material, that is to sayit is enclosed in its pores. The precursor is then transformed orconverted into the material to be produced. Preferably, the precursor issuch a material or has such a composition that, at high temperatures,the material to be produced forms. If, for example, metal oxides are tobe produced, the precursor used can be, for example, nitrates thereofwhich, at elevated temperatures, transform into the oxides. The materialto be produced is, according to the invention, heated in the presence ofthe matrix material to a temperature which is above the later servicetemperature. A good thermal stability of the resultant materials isachieved when thermal treatment is at a temperature more than 100° C.above the later service temperature. Preferably, the thermal treatmentis performed over a period such that the surface area of the material tobe produced does not change at all, or changes as little as possible.

For the production of the inventive materials, first a thermalpretreatment is carried out under protective gas at very hightemperatures, markedly (50° C., better 100° C. or more) above the laterservice temperature of the materials, to avoid premature combustion ofthe matrix material, for example the activated carbon matrix. It hasbeen found that as a result of the very high temperatures during thetreatment, the materials produced in the matrix are passivated. It isalso possible to produce the thermodynamically most stable phases. Afterthe thermal pretreatment, the matrix material, such as activated carbon,can be burnt off at lower temperatures under a reactive gas atmosphere,for example in the presence of oxygen, as a result of which the desiredmaterial remains behind. If silica gels are used as matrix materials,these can be dissolved, for example, with HF or NaOH, and thus removed.The description of this methodology is intended only to illustrate theprocedure by way of example, and in no way to restrict it. Matricesother than activated carbon can also be used, or methods other thancalcination can be used for matrix removal. To produce ordered thermallystable oxides, it has proved to be preferred to use matrix materialshaving what is termed an ordered pore structure, that is to saymaterials having a pore structure as uniform as possible. Examples whichmay be mentioned are, for example, ordered carbons such as CMK-1, SNU-1,or silica materials, such as CMK-3, or ordered silica gels, such asSBA-15 or MCM-48. Those skilled in the art are able here to make anappropriate method and material selection. By selecting appropriatematrix materials it is possible to set the particle size of theinventively available particles, in particular to set an upper limit.The material having a high specific surface area preferably has a highthermal stability, so that it can be used in processes which are carriedout at high temperatures. Examples of such materials are metal oxides.In particular the materials produced according to the invention arepreferably oxides having high melting points, for example above 1500° C.Oxides which can be used are oxides of the elements Be, Mg, Ca, Sr, Ba,Al, Ga, Si, Mg, Ca, Sc, Y, La, Ti, Zr, Hf, V, Cr, Mn, Fe, Co, Ni, Zn, U,Th and the lanthanides or mixtures thereof. The oxides producedaccording to the invention preferably have a surface area greater than10 m²/g, in particular greater than 50 m²/g. It is possible to produce,for example, γ-aluminum oxide which, even after thermal treatment for aperiod of 3 h at 1100° C. in the presence of air, has a specific surfacearea of at least 50 m²/g. Zirconium oxides can verify reference examplesthat the surface areas which are achievable using conventional methods,that is to say without high-temperature treatment, are markedly smaller.In addition, it is possible to obtain ZrO₂ and oxide mixtures having amolar fraction of ZrO₂ greater than 50% which, after thermal treatmentin air at 1000° C. for a period of 3 h, still have a specific surfacearea of at least 10 m²/g. MgAl₂O₄ obtainable according to the invention,for example, after thermal treatment in air at 750° C. for 1 h still hasa specific surface area of at least 50 m²/g.

The invention further relates to materials having high specific surfaceareas which are obtainable by the method described above.

Because of their thermal stability, the inventive materials aresuitable, for example, as support materials for catalysts, such ascatalysts which are used at high temperatures. A possible field of useis motor vehicle catalysts which are used at operating temperaturesbetween about 300 and 600° C.

The inventive method is, furthermore, suitable for directly producingsupported catalysts having a metal component and an oxide support. Inthis embodiment, a suitable metal component is added to the productionmethod, which then, after tempering, is present in the form of smallmetal particles in high dispersion on the oxide support material. Themajority of the particles are preferably less than 20 nm in size.However, supported catalysts can also be produced in which the majorityof the metal particles are smaller than 5 nm, or even smaller than 2 nm.The metal component, if appropriate, can be obtained by a reduction stepfrom oxide particles of the corresponding sizes.

EXAMPLES

These examples are intended only to illustrate the method and in no wayto restrict it. Those skilled in the art are able, by a suitableselection of precursor compounds, matrices and treatment conditions, toproduce other materials also having a high specific surface area andhigh thermal stability.

According to the inventive method, an activated carbon was impregnatedwith concentrated aluminum nitrate solution and the sample was thenheated at 1300° C. under argon. Alternatively, other protective gasescan also be used, for example other noble gases. The use of nitrogencan, in the case of aluminum oxide, lead to the formation of aluminumnitride, but nitrogen can be used as protective gas with other oxides.Those skilled in the art are able to make a suitable selection. Thecomposite of carbon and the decomposition product of the aluminumnitrate, in an X-ray diffraction experiment, exclusively showed verybroad reflections, which, surprisingly, cannot be assigned to α-aluminumoxide which is usually formed at temperatures above 1100° C., but toγ-aluminum oxide. The aluminum oxide which remains after the combustionof the carbon at 500° C. and subsequent tempering for 45 minutes at 600°C. has a specific surface area of 198 m²/g. After tempering at 1200° C.for 4 h, a mixture of alpha- and gamma-aluminum oxide is formed having aspecific surface area of 14 m²/g. A pyrolysis of the aluminumnitrate-impregnated carbon at 1300° C. with access of air, in contrast,leads directly to alpha-aluminum oxide having a surface area of 1.8m²/g. The advantage of the inventive method is clearly shown thereby.

As an example of materials which consist of mixtures of oxides, themethod was applied to the mixture of ZrO₂/CeO₂, with a predominant ZrO₂fraction. It was found that the resulting mixtures, after tempering for3 hours at 1000° C. in the presence of air, still have a specificsurface area of greater than 10 m²/g (examples 10-12).

By suitable choice of precursors, ternary oxides, such as MgAl₂O₄,having a high specific surface area and extreme thermal stability arealso accessible. Here also, surface areas of greater than 150 m²/g arestill achievable after tempering for 1 h at 750° C. in air (examples7-9).

An MgAl₂O₄ spinel was produced by impregnating activated carbon withappropriately concentrated precursor solutions and tempering the carbonat 800° C. under protective gas. After combustion of the carbon at 500°C., the spinel had a specific surface area of 209 m²/g, and aftertempering at 750° C. for 1 h the specific surface area was still 158m²/g.

A sample impregnated with aluminum precursor and iridium(III)acetylacetonate was first heated at 1100° C. under protective gas. Aftercombustion of the carbon in air at 500° C., a bluish-gray powderremained having a specific surface area of 323 m²/g. In the X-raydiffractogram, broad reflections of gamma-aluminum oxide and IrO₂ couldbe recognized. In the transmission electron microscope, particles ofiridium and iridium oxide were to be seen at a size of about 1 nmdispersed over the entire aluminum oxide matrix, in addition to a fewlarge particles having a size of about 50 nm.

Example 1 Impregnation of the Carbon with Aluminum Nitrate

58.87 g of Al(NO₃)₃.9H₂O were dissolved in 28.95 g of distilled water.24 ml of this solution were admixed with 6.0 g of a vacuum-dehydratedactivated carbon powder (Fluka 05120) and stirred for 10 min using amagnetic stirrer bar. The batch was then filtered off by suction invacuo and the filter cake was mechanically pressed and dried for 1 h at80° C. in a circulation oven.

Weight obtained: 17.4 g

Example 2 Aluminum Oxides after Calcining at 800° C. Under ProtectiveGas

4.2 g of the impregnated carbon from example 1 were charged into aquartz combustion boat and introduced into a quartz tube. The quartztube was flushed with argon and heated to 800° C. in a tubular furnaceat a heating rate of 4° C./min under a steady argon stream, andmaintained at this temperature for 30 min. After the quartz tube wascooled to room temperature, the material was brought into contact withair and weighed.

Weight obtained: 1.31 g of a black powder

Pyrolysis of the carbon matrix: 1.13 g of the black powder were chargedinto an open quartz crucible and pyrolyzed in a muffle furnace with aircontact for 2 hours at 500° C. (heating rate 4° C./min).

Weight obtained: 0.29 g of a virtually white powder

XRD: gamma-aluminum oxide

BET surface area: 356 m²/g

0.14 g of the material pyrolyzed at 500° C. were charged into an openquartz crucible and tempered for 15 hours at 1100° C. in a mufflefurnace with air contact (heating rate 4° C./min).

Weight obtained: 0.14 g of a white powder)

XRD: gamma-aluminum oxide

BET surface area: 61 m²/g

Example 3 Aluminum Oxides after Calcining at 1100° C. Under ProtectiveGas

4.45 g of the impregnated carbon from example 1 were, as described inexample 2, calcined under argon for 30 min at 1100° C.

Weight obtained: 1.32 g of a black powder

1.11 g of the black powder were pyrolyzed in the muffle furnace for 3 hat 500° C. with air contact.

Weight obtained: 0.28 g of a light-beige powder XRD: gamma-aluminumoxide

BET surface area: 323 m²/g

0.16 g of the light-beige powder were tempered for 1 h at 800° C. withair contact.

Weight obtained: 0.16 g

XRD: gamma-aluminum oxide

BET surface area: 241 m²/g

0.10 g of the light-beige powder pyrolyzed at 500° C. were tempered for3 h at 1100° C. with air contact.

Weight obtained: 0.09 g of white powder

XRD: gamma-aluminum oxide

BET surface area: 86 m²/g

Example 4 Reference Experiment 1

2.95 g of the impregnated carbon from example 1 were charged into aquartz crucible and calcined for 30 min at 1100° C. with air contact(heating rate 4° C./min).

Weight obtained: 0.22 g of white powder

XRD: gamma-aluminum oxide

BET surface area: 39 m²/g

0.15 g of the white powder were tempered for 3 h at 1100° C. with aircontact.

Weight obtained: 0.15 g of white powder

XRD: alpha- and gamma-aluminum oxide

BET surface area: 38 m²/g

Example 5 Reference Experiment 2

1.5 ml of the aqueous aluminum nitrate solution described under example1 were calcined for 30 min at 1100° C. with air contact (withoutactivated carbon!)—heating rate 4° C./min—

Weight obtained: 0.19 g of a white powder

XRD: alpha-aluminum oxide

BET surface area: 1.2 m²/g

Example 6 Aluminum Oxides after Calcining at 1300° C. Under ProtectiveGas

131 mg of the impregnated carbon from example 1 were held at 1300° C.for 2 hours under argon in a Thermal Analysis Unit from Netzsch (heatingrate 4° C./min).

Pyrolysis of the carbon matrix: 3 h at 500° C. and 45 min at 650° C. inthe muffle furnace with air contact.

Weight obtained: 0.03 g of a white powder

XRD: gamma-aluminum oxide

BET surface area: 198 m²/g

Study of Thermal Stability

Approximately 20 mg of the white powder were tempered for 4 h at 1200°C. with air contact.

Weight obtained: 18 mg of white powder

XRD: gamma- and alpha-aluminum oxide

BET surface area: 14 m²/g

Example 7 Reference Experiment 3

1.56 g of the impregnated carbon from example 1 were charged into aquartz crucible and calcined at 1300° C. with air contact in ahigh-temperature muffle furnace for 2 h (heating rate 4° C./min).

Weight obtained: 0.18 g of white powder

XRD: alpha-aluminum oxide

BET surface area: 1.8 m²/g

Comparison of example 6 with example 7 shows that even after arelatively long thermal load of the material, the oxide produced by theinventive method has a markedly higher specific surface area than thematerial known from the prior art.

Example 8 Impregnation of a Carbon with Magnesium Nitrate and AluminumNitrate

10.0 g of Mg(NO₃)₂.6H₂O and 29.26 g of Al(NO₃)₃.9H₂O were dissolved in13.3 g of distilled water to give a colorless solution.

14 ml of this solution were admixed with 4.05 g of an activated carbonpowder (Fluka 05120) dehydrated in vacuo, stirred at room temperaturefor 10 min, filtered off by suction in vacuo and the filter cake wasmechanically pressed. The impregnated carbon was dried for 30 min at 80°C. in a circulation oven.

Weight obtained: 9.8 g of a black powder

Example 9 MgAl₂O₄ after Calcining at 800° C. Under Protective Gas

2.30 g of the impregnated carbon from example 7 were, as described inexample 2, calcined for 1 h at 800° C. under argon in the tubularfurnace.

Weight obtained: 0.86 g of black powder

Pyrolysis of the carbon matrix: 0.79 g of the black powder werepyrolyzed for 2 h at 500° C. in the muffle furnace with air contact(heating rate 4° C./min).

Weight obtained: 0.25 g of a light-beige powder

BET surface area: 209 m²/g

0.15 g of the light-beige powder were tempered for 1 h at 750° C. withair contact in the muffle furnace.

Weight obtained: 0.15 g of white powder

XRD: broad spinel reflections

BET surface area: 158 m²/g

Example 10 Reference Experiment 4

1.81 g of the impregnated carbon from example 7 were calcined for 1 h at800° C. in the muffle furnace with air contact (heating rate 4° C./min).

Weight obtained: 0.20 g of white powder

XRD: broad spinel reflections

BET surface area: 103 m²/g

Example 11 Impregnating a Carbon with Zirconyl Nitrate and CeriumNitrate

20 ml of a 35% strength by weight ZrO(NO₃)₂ solution in dilute HNO₃(Aldrich) were mixed with 12.5 ml of a 1.5 molar Ce(NO₃)₄ solution (AlfaAesar) (molar ratio Zr:Ce=70:30). 10 ml of this mixture were admixedwith 2.40 g of an activated carbon (Fluka 05120) dehydrated in vacuo,stirred for 10 min at room temperature, filtered off by suction invacuo, mechanically pressed and dried for 1 h at 80° C. in thecirculation oven.

Weight obtained: 4.5 g of a black powder

Example 12 ZrO₂/CeO₂ after Calcining at 1100° C. Under Protective Gas

2.6 g of the impregnated carbon from example 10 were calcined for 30 minat 1100° C. under protective gas in the tubular furnace, as described inexample 2 (heating rate 4° C./min).

Weight obtained: 1.47 g of black powder

Pyrolysis of the carbon matrix: 1.19 g of the black powder werepyrolyzed for 2 h at 500° C. in the muffle furnace with air contact(heating rate 4° C./min).

Weight obtained: 0.47 g of light-yellow powder

XRD: tetragonal zirconium oxide, broad reflections

BET surface area: 149 m²/g

0.18 g of the light-yellow powder were tempered for 3 h at 1000° C. inthe muffle furnace with air contact (heating rate 4° C./min)

Weight obtained: 0.17 g of light-yellow powder

XRD: tetragonal zirconium oxide

BET surface area: 14.5 m²/g

Example 13 Reference Experiment 5

1.40 g of the impregnated carbon from example 10 were calcined at 1100°C. for 30 min in the muffle furnace with air contact (heating rate 4°C./min).

Weight obtained: 0.26 g of light-yellow powder

XRD: tetragonal zirconium oxide, possibly Zr_(x)Ce_(y)O₂

BET surface area: 2.7 m²/g

Example 14 Impregnation of a Carbon with Chromium Nitrate

20.5 g of Cr(NO₃)₃.9H₂O (Fluka) were dissolved in 10 g of distilledwater to give a deep-blue solution. 6.0 ml of the solution were admixedwith 1.67 g of an activated carbon (Fluka 05120) dehydrated in vacuo andstirred at room temperature for 20 min. The batch was then filtered offby suction in vacuo, the filter cake was mechanically pressed and driedfor 1 h at 80° C. in the circulation oven.

Example 15 Cr₂O₃ by Calcining at 450° C. Under Argon

The carbon impregnated under example 13 was transferred to a quartzcombustion boat and calcined in a tubular furnace, and the carbon matrixwas pyrolyzed. For this the material was heated to 450° C. under argon(heating rate 3° C./min) and calcined for 30 min under a steady argonstream. Then, at a constant furnace temperature, by introducing anargon-air mixture, the carbon matrix was combusted. By setting the airfraction, the sample temperature was a maximum 500° C. during the 1-hourcourse of pyrolysis.

Weight obtained: 0.52 g of green powder (sample was pyrophoric on firstair contact.)

XRD: Cr₂O₃ (eskolaite)

BET surface area: 156 m²/g

Example 16 Reference Experiment 6

A carbon impregnated with Cr(NO₃)₃ (preparation as described in example13, 1.61 g of activated carbon+6 ml of chromium(III) nitrate solution)was calcined for 1 h at 450° C. in the muffle furnace with air contactin an open porcelain dish.

Weight obtained: 0.51 g of grayish-green powder

BET surface area: 70 m²/g

Example 17 Impregnation of a Carbon with Aluminum Nitrate andIridium(III) Acetylacetonate

2.70 g of the carbon impregnated with Al(NO₃)₃ from example 1 wereadmixed with a solution of 30 mg of iridium(III) acetylacetonate(Aldrich) in 1.5 ml of tetrahydrofuran, sitrred intensively and lightlyground in a mortar.

Weight obtained: 3.5 g of black powder

Example 18 Ir/Al₂O₃ by Calcining at 1100° C. Under Protective Gas

1.69 g of the impregnated carbon from example 16 were calcined for 30min at 1100° C. under argon in the tubular furnace, as described inexample 2 (heating rate 4° C./min).

Weight obtained: 0.76 g of a black powder

Pyrolysis of the carbon matrix: 0.69 g of the black powder was pyrolyzedfor 2 h at 500° C. in the muffle furnace with air contact (heating rate4° C./min).

Weight obtained: 0.19 g of bluish-gray powder

XRD: gamma-Al₂O₃ and broad IrO₂ reflections

BET surface area: 323 m²/g

TEM analysis: Uniform distribution of IrO₂ particles of size from 1 to1.5 nm in the total sample, in addition, IrO₂ particles up toapproximately 50 nm in size are situated on the surface.

80 mg of the bluish-gray powder were tempered for 3 h at 1000° C.(heating rate 4° C./min) in the muffle furnace with air contact.

Weight obtained: 70 mg of bluish-gray powder

BET surface area: 151 m²/g

Example 19 Reference Experiment 7

1.69 g of the impregnated carbon from example 16 was calcined for 30 minat 1100° C. in the muffle furnace with air contact (heating rate 4°C./min).

Weight obtained: 0.19 g of light grayish-green powder

XRD: gamma-aluminum oxide and sharp Ir+IrO₂ reflections

BET surface area: 92 m²/g

TEM: Ir/IrO2 particles approximately 20 to 500 nm in size, no particlesin the 1 to 1.5 nm range

0.08 mg of the light grayish-green powder was tempered for 3 h at 1000°C. in the muffle furnace with air contact (heating rate 4° C./min).

Weight obtained: 0.08 g of light-gray powder

XRD: sharp IrO₂ reflections

BET surface area: 95 m²/g

Example 20 Impregnation of a Carbon with Zirconyl Nitrate

11.0 g of an activated carbon (Fluka 05120) dehydrated in vacuo wereadmixed with 18 ml of a ˜35% strength by weight ZrO(NO₃)₂ solution indilute nitric acid (Aldrich), stirred intensively and lightly ground ina mortar. The resultant material was dried for 20 h at room temperature.

Example 21 Zirconium(IV) Oxide after Calcining at 1100° C. UnderProtective Gas

18.2 g of the impregnated carbon from example 19 were, as described inexample 2, calcined for 30 min at 1100° C. under argon in the tubularfurnace. The remaining black powder was then pyrolyzed for 1 h at 650°C. with air contact in the muffle furnace (heating rate 4° C./min).

Weight obtained: 3.5 g of a weakly beige-pink powder

XRD: ZrO₂ reflections

BET surface area: 110 m²/g

1. A method for producing a material having a high specific surface areaat high service temperature, the material, embedded in a matrix,selected from finely divided carbonaceous materials and/or silica gels,preferably being produced by thermal pretreatment, and the matrix thenbeing removed, wherein the thermal pretreatment comprises heating to atemperature which is above the service temperature.
 2. The method asclaimed in claim 1, wherein the size of the material particles producedis upwards-limited by the matrix.
 3. The method as claimed in claim 1,wherein the heating temperature is more than 100° C. above the servicetemperature.
 4. The method as claimed in claim 1, wherein the matrix offinely divided carbonaceous materials is selected from activated carbonand ordered carbons.
 5. The method as claimed in claim 4, wherein thethermal pretreatment is performed under protective gas, and the carbonmatrix is removed by a reactive gas atmosphere after the thermalpretreatment at a lower temperature.
 6. The method as claimed in claim5, wherein the reactive gas atmosphere comprises oxygen.
 7. The methodas claimed in claim 1, wherein the material is an oxide.
 8. The methodas claimed in claim 7, wherein the oxide has a melting point above 1500°C.
 9. The method as claimed in claim 7, wherein the oxide is an oxide ofthe elements Be, Mg, Ca, Sr, Ba, Al, Ga, Si, Mg, Ca, Sc, Y, La, Ti, Zr,Hf, V, Cr, Mn, Fe, Co, Ni, Zn, U, Th or the lanthanides or a mixture ofsuch oxides.
 10. A material having a high specific surface area at highservice temperature, which material is obtainable by the means that thematerial, embedded in a matrix selected from finely divided carbonaceousmaterials and/or silica gels, is preferably produced by thermalpretreatment, and the matrix is then removed, the thermal pretreatmentcomprising a heating to a temperature which is above the servicetemperature.
 11. The material as claimed in claim 10, which afterthermal treatment in air at 1000° C. over a period of 3 h, still has aspecific surface area of at least 10 m²/g.
 12. A supported catalystcomprising the material as claimed in of claim
 10. 13. The material asclaimed in claim 10 which comprises an oxide component and a metalcomponent, the particles of the metal component having in the majoritysizes less than 20 nm, and the metal component, optionally, beingfurther able to be obtained by a reduction step from oxide particles ofthe corresponding sizes.
 14. The material as claimed in claim 10 whichcomprises particles of the metal component having in the majority sizesless than 5 nm.
 15. The material as claimed in claim 11, which, afterthermal treatment in air at 1000° C. over a period of 3 h, still has aspecific surface area of at least 50 m²/g.
 16. The material as claimedin claim 14, which comprises particles of the metal component having inthe majority sizes less than 2 nm.
 17. A method of producing a materialhaving a high specific surface area at a high service temperature, saidmethod comprising the following steps: (a) producing the materialembedded in a matrix by thermal pretreatment, the matrix being selectedfrom the group consisting of finely divided carbonaceous materials,silica gels, and mixtures thereof; and (b) removing the matrix; whereinthe thermal pretreatment comprises heating to a temperature which isabove the service temperature.